ORNL hits plutonium mark


Oak Ridge National Laboratory announced it had achieved production of 50 grams of plutonium-238.That’s roughly the size of a golf ball, but it’s considered a milestone in re-establishing a U.S. stockpile of Pu-238 for use as a powersource on deep-space missions.

ORNL has been developing the capability over the past couple of years with funding that NASA provided via the Department of Energy’s Office of Nuclear Energy.

The lab uses the High Flux Isotope Reactor for production of the plutonium isotope and then processes and purifies the radioactive material in a series of shielded hot cells.

Pu-238, a different isotope from the plutonium- 239 used in nuclear weapons, is used as fuel in space power systems known as radioisotope thermoelectric generators or RTGs. The radioactive material produces heat as it decays, and that heat is converted to electricity for vital tasks on spacecraft.

ORNL said the infrastructure is now in place to provide a steady and growing supply of plutonium- 238 for future space missions. According to NASA, the next space mission with plans for using an RTG is the Mars 2020 Rover, which is tentatively scheduled for launch in July 2020.

“The mission seeks signs of life on Mars and will test technology for human exploration and gather samples of rocks and soil that could be returned to Earth,” the statement said.

Oak Ridge National Laboratory does the work in conjunction with other DOE labs. Idaho National Laboratory provides the inventory of neptunium-237 to ORNL, which fabricates the material — mixed with aluminum — into targets. Those targets are irradiated inside the reactor to produce the plutonium.

Officials said the project has restored a domestic capability for producing Pu-238 for the first time in nearly 30 years. The previous U.S. source at DOE’s Savannah River Plant in South Carolina was shut down in the late 1980s.

Bob Wham, who headed the project at Oak Ridge, said in a statement, “Once we automate and scale up the process, the nation will have a long-range capability to produce radioisotope power systems such as those used by NASA for deep-space exploration.”

The lab expects to produce 300 to 400 grams of Pu-238 per year and eventually ramp up annual production to about 1.5 kilograms.

“We have demonstrated that our process works, and we are ready to move on to the next phase of the mission,” Wham said.

After the neptunium has been irradiated in the High Flux Isotope Reactor to form Pu-238, the pellets are removed and dissolved to separate the plutonium from what’s left of the neptunium.

The plutonium product is converted to an oxide and shipped to Los Alamos National Laboratory in New Mexico, where it’s stored until needed for a space mission.

The current U.S. inventory of plutonium-238 is only about 35 kilograms, according to DOE. That includes material that’s leftover from the Savannah River production decades ago, as well as Pu-238 purchased from Russia.

Source: Knoxville News Sentinel, by Frank Munger

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